WO2013174609A1

WO2013174609A1 - Asymmetrical multi-layered membrane for electroacoustic transducers

Info

Publication number: WO2013174609A1
Application number: PCT/EP2013/058582
Authority: WO
Inventors: Bernhard MÜSSIG; Yeliz Tepe; Michael Egger
Original assignee: Tesa Se
Priority date: 2012-05-21
Filing date: 2013-04-25
Publication date: 2013-11-28
Also published as: TWI597165B; CN104335603A; KR20150011007A; EP2853100A1; US9796160B2; EP2853100B1; DE102012208477A1; IN2014DN10265A; KR101933983B1; CN104335603B; TW201412530A; US20150125692A1; JP2015526924A; JP6148726B2; MX2014013722A

Abstract

The invention relates to a multi-layered laminate for producing membranes for electroacoustic transducers, comprising a first layer (3) consisting of a polyether ether ketone film having a heat of crystallisation of at least 15 J/g, determined in the first heating curve of the dynamic differential calorimetric measurement, a second layer (1) consisting of a thermoplastic plastic film having a heat of crystallisation of no more than 5 J/g, determined in the first heating curve of the dynamic differential calorimetric measurement, and an adhesive layer (2) arranged between the first (3) and second (1) layers. Alternatively, the first (3) and second (1) layers are defined by their shrinkage properties after 15 minutes at 200 °C: the first layer (3) has shrinkage of more than 10% in at least one direction, and the second layer (1) has shrinkage of less than 10% in the longitudinal and transverse directions. A laminate constructed in this manner is characterised by lower fold formation when said laminate is processed using multi-cavity thermoforming.

Description

description

Asymmetric multilayer membrane for electroacoustic transducers

The invention relates to an asymmetric multilayer laminate for use as a membrane for electroacoustic transducers and to a method for producing this multilayer laminate.

With the general trend towards smaller and more compact devices in the field of consumer electronics, the speakers in mobile phones, smartphones, headphones, personal digital assistants (PDAs), notebooks etc. inevitably have to become smaller and smaller. As a result, increasingly higher demands are placed on the membranes of such microspeakers, whose size is typically in the range of 20 mm ² to 900 mm ² , with regard to the acoustic properties and the service life.

In general, the material of a loudspeaker membrane should at the same time be as stiff, light and well damped as possible. These requirements arise from the fact that the frequency at which the membrane breaks up into partial vibrations and from which it increasingly produces resonances and distortions, is proportional to (E / p) ^{0 5} , where E denotes the elastic modulus and p the density of the membrane , As the factor (E / p) ^{0 5 increases} , the upper limit of the frequency range of the loudspeaker can thus be increased. Further advantages of a light and at the same time stiff diaphragm are a fast acceleration of the diaphragm during the impulse transition and thus a higher achievable sound pressure. On the other hand, the diaphragm should simultaneously have a high internal damping tan δ for lowering the resonance frequency f ₀ and suppression of resonance peaks in the frequency response. Since the criteria are stiff, light and well damped but constructively contradictory, must in speaker membranes always a certain compromise with respect to the membrane material to be received or a combination of stiff and damping layers are selected.

The most common membrane materials are paper, metal and plastic, which are often coated or modified to meet these requirements as much as possible. Paper has a low density and good damping, the lack of rigidity can be improved for example by reinforcement with glass or Kevlar fibers. Metals have a high stiffness, but are usually poorly damped, which often results in a clinking and a sharp, metallic sound. The damping of metal foils (aluminum, titanium, beryllium) can be improved by e.g. Composites with a middle layer of soft polymers or damping foams are produced. Plastic membranes have the advantage that they cover a very wide range of soft, well-damped polymers to very stiff materials with low attenuation and can be selected suitable for different applications. Such plastic membranes are based either on impregnated fiber webs or on films whose stiffness or damping properties are often optimized by combination with stiff or cushioning layers. For example, EP 2 172 059 A describes a 5-layer loudspeaker membrane in which one rigid polyetheretherketone film is bonded to one side on both sides of a damping carbon fiber nonwoven via a respective thermoplastic adhesive layer. In US 201 1 - 0272208 A, a 5-ply laminate is described in which rigid outer layers are applied to both sides of an adhesive-coated polyethylene terephthalate support. US Pat. No. 7,644,801 A mentions a 3-layer laminate composed of 2 polyarylate films and an intermediate acrylate adhesive, which wrinkles and wrinkles significantly less than pure polyarylate films.

These examples show that multilayer laminates are in principle well suited as loudspeaker membranes, despite the large number of different variants an optimal solution has not yet been found.

Because of the strong heating of the membranes of microspeakers in operation for these often rigid films of high temperature resistant plastics such Polyetheretherketone (PEEK), polyether ketone (PEK), polyether ketone ketone (PEKK), polyarylate (PAR), polyetherimide (PEI), polyphenylene sulfide (PPS), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT) or aramides used. The microspeaker membranes are formed either directly from such films or from multilayer laminates of these films with additional cushioning layers. As used herein, the term membrane means the membrane formed from foils or film composites as used in the finished loudspeaker. As used herein, the term multi-layer laminate refers to a composite of at least two films and additional layers lying between these films, from which the actual speaker membrane is formed.

Polyetheretherketone membranes, hereafter called PEEKs, have outstanding temperature resistance and perform best in loudspeaker manufacturers' increasingly important high-performance endurance tests, which is why micro loudspeakers are showing a clear trend towards the use of PEEK. Due to the high rigidity of PEEK, there is great interest in membranes made of PEEK multi-layer laminates with additional damping layers for the reasons mentioned above. The PEEK films used to make the multilayer laminates are commercially available in both amorphous and partially crystalline versions. Amorphous or substantially amorphous PEEK films are cooled during their preparation as quickly to temperatures below the glass transition temperature T _g, that the material can not form a substantially crystalline regions. These substantially amorphous PEEK films do not crystallize on heating above the glass transition temperature during shaping of the membrane by deep drawing or embossing. In contrast, partially crystalline PEEK films already have a crystalline content after their preparation. A substantially amorphous PEEK film can be distinguished from a partially crystalline PEEK film by differential scanning calorimetry (DSC).

DSC measurements on amorphous and semicrystalline PEEK films were carried out with the measuring device DSC 204 F1 from Netzsch. For this purpose, about 5 mg of the film was weighed into a 25 μί aluminum crucible with perforated lid and heated at a heating rate of 10 K / min from 20 ° C to 410 ° C. The recorded or emitted heat is recorded and the resulting curve referred to as the first heating curve. It was then cooled at a cooling rate of 10 K / min back to 20 ° C and thereby recorded the cooling curve. Finally, a second heating curve was recorded by heating a second time from 20 ° C to 410 ° C at a heating rate of 10 K / min.

The two film types differ in that amorphous PEEK films measured under these conditions exhibit a significant exothermic crystallization peak in the first heating curve, which is absent in the partially crystalline PEEK film. A substantially amorphous in the context of this invention PEEK film is characterized in that it shows a heat of crystallization of at least 15 J / g (ie 15 J / g or more) under the above DSC measurement conditions in the first heating curve. A partially crystalline PEEK film according to this invention is characterized in that it exhibits a heat of crystallization of at most 5 J / g (ie, 5 J / g or less) under the above-mentioned DSC measuring conditions in the first heating curve. This upper limit is given due to potential fluctuations of the baseline during the measurement, as a rule, no crystallization peak is observed in the first heating curve of the semicrystalline PEEK film. Due to the better processability during shaping, multilayer laminates of amorphous PEEK films are predominantly used for loudspeaker membranes. These multilayer laminates are crystallized during thermoforming or thermoforming at temperatures above the glass transition temperature of 143 ° C. As a result, the PEEK films are present in the finished membrane in a partially crystalline state and thus provide for a subsequently higher rigidity and strength of the membrane.

In the process of deep drawing, the thickness of the deep-drawn membrane can be adjusted very well by the process conditions, from a PEEK multilayer laminate with a given total thickness, different membrane thicknesses can be produced and adapted to the requirements of different speaker designs. The disadvantage of this process is a high reject rate, since depending on the degree of deep-drawing, only a very small proportion of the multi-layer laminate used ends up in the finished membrane. This makes thermoforming just for the very expensive PEEK films not economical. In the multicavity thermoforming process, a much larger fraction of the multilayer laminate terminates in the membrane, but there is little latitude in the variation of its thickness. Since the resonant frequency of the membrane is proportional to its total thickness, to achieve low resonance frequencies during thermoforming, thin multi-layer laminates and thus also thin PEEK films must be used from the outset. The thinnest commercially available amorphous PEEK films are currently 6 μm thick. Despite the great interest in multi-layer laminates from these films, they could not be used until now, because during the multicavity thermoforming, the side facing up in the thermoform and the air facing throws strong wrinkles.

Surprisingly, it has now been shown that the problem of wrinkling is remedied if the thermoforming upwardly amorphous PEEK film is replaced by a partially crystalline PEEK film. By using such an asymmetric multi-layer laminate of a substantially amorphous PEEK film, adhesive layer and partially crystalline PEEK layer, it is thus possible to produce thin membranes from PEEK multilayer laminates by means of the multicavity thermoforming process.

In fact, it has been found that other materials, which either can not crystallize or are already fully crystallized, can replace one of the two amorphous PEEK films. The subject of the invention is therefore multi-layer laminate for the production of membranes for electroacoustic transducers

a) a first layer (in the context of this document referred to as "first cover layer") of a polyetheretherketone film (PEEK film) having a heat of crystallization of at least 15 J / g (ie 15 J / g or more, heat of crystallization Q _Kr ^ 15 J / g), determined in the first Aufheizkurve the differential scanning calorimetry - ie a substantially amorphous PEEK film -, b) further comprises a second layer (referred to in the context of this layer as a "second cover layer") of a thermoplastic film with a heat of crystallization of at most 5 J / g (that is, 5 J / g or less, heat of crystallization Q _Kr ^ 5 J / g) determined in the first heating curve of the differential scanning calorimetry measurement - that is, a film which is in the Is substantially unable to crystallize or to any further crystallization, -, and

c) an adhesive layer disposed between the first and second cover layers. The multilayer laminate may be limited to the three layers mentioned, but may also have further layers in the laminate structure.

A 3-layer laminate of partially crystalline PEEK film (1), adhesive (2) and amorphous PEEK film (3) is shown by way of example in FIG. 1.

Particularly suitable according to the invention in the sense of the second cover layer is a partially crystalline PEEK film, ie a PEEK film which has a heat of crystallization of at most 5 J / g determined in the first heating curve of the differential scanning calorimetry measurement.

Further films suitable for the purposes of the invention for use as a second cover layer - ie as a replacement for one of the two amorphous PEEK films of conventional constructions - are, for example, films of polyphenylene sulfide (PPS), polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polybutylene terephthalate (PBT ), Polyarylate (PAR), polyimide (PI), polyetherimide (PEI), polyphenylsulfone (PPSU), polyethersulfone (PES) or polysulfone (PSU).

Preferably, films are used as the second cover layer, the thicknesses in the range of 1 μηη to 50 μηη, preferably from 2 μηη to 40 μηη, more preferably from 5 μηη have up to 15 μηη.

The amorphous PEEK films for the first cover layer in the asymmetric multilayer laminate also have thicknesses in the range from 1 μm to 50 μm, preferably from 2 μm to 40 μm, particularly preferably from 5, independently of the thicknesses of the films for the second cover layer μηη to 15 μηη on.

The amorphous first cover layer and the second, non-crystallizable cover layer can be selected to be the same thickness. A comparison of the properties of the above-mentioned, usable as a second cover layer films with the commercially available amorphous PEEK film has shown that the shrinkage of non-crystallizable films, in particular films of the aforementioned materials having a heat of crystallization of at most 5 J / g, significantly lower as the shrinkage of the amorphous PEEK film. Table 1 shows comparative values by way of example.

Table 1. Shrinkage of various films at 200 ° C and 15 min.

The invention therefore furthermore relates to a multilayer laminate for the production of membranes for electroacoustic transducers, comprising a first cover layer which, after 15 minutes at 200 ° C., has a shrinkage greater than 10% in at least one direction, arranged between the first and second cover layers Adhesive layer and a second cover layer, which after 15 minutes at 200 ° C in the longitudinal and transverse directions each have a shrinkage of less than 10%, preferably less 5%. Such films are preferably used as films for the first and the second cover layer, as described in more detail in this specification, the statements relating to these films apply correspondingly to this multilayer laminate. The shrinkage of the films is determined by two marks at a distance of 10 cm are made on the film at room temperature with a film pen and the films are stored in a convection oven at 200 ° C freely suspended for 15 minutes. After cooling, the distance between the two markings is measured again and the percentage change in the distance is determined. This measurement is carried out both in the longitudinal direction of the film - also called Machine Direction or MD - as well as in the transverse direction of the film - also called Transverse Direction or TD - to detect the different shrinkage depending on the orientation. In the multilayer laminate according to the invention, an intermediate layer of an adhesive is arranged between the amorphous PEEK film and the partially crystalline PEEK film. The purpose of this layer is to stably bond the films above and below and to dampen the vibration of the stiff outer films. Suitable adhesives are polyacrylates dissolved in solvents or aqueous polyacrylate dispersions and rosin-modified natural and synthetic rubber. Particularly suitable are dissolved polyacrylate adhesives.

The adhesive layer is preferably coated from solvent or from water with the aid of a nozzle or a doctor blade on the first cover layer - in particular on an amorphous PEEK film of thickness 6 μηη to 12 μηη - and then for 5 to 30 minutes at 100 to 170 ° C dried. On the dried adhesive is then the second cover layer - in particular a partially crystalline PEEK film thickness of 6 μ to 12 μηη, preferably 8 μηη - laminated or laminated.

The layer thickness of the adhesive after drying is 2 μηη to 100 μηη, preferably 5 μηη to 50 μηι, more preferably 10 μηη to 30 μηι.

The multilayer laminates according to the invention can be used outstandingly in a process for the production of membranes for electroacoustic transducers, wherein they are subjected to the process of multicavity thermoforming. In this method, the multilayer laminate is placed on the heatable thermoforming, which contains recesses with the negative impression of the membrane to be formed. Subsequently, the multi-layer laminate is heated, for example by IR radiation and thereby softened and then pressed from above with compressed air into the recesses. Alternatively, the softened multi-layer laminate can also be pressed into the molds with a stamp made of silicone or foamed silicone. The membranes produced by this method according to the invention showed significantly less wrinkling than membranes of two 6 to 9 μm thick amorphous PEEK films with intervening adhesive layer.

An advantageous arrangement of the laminate according to the invention in the thermoforming is shown in FIG. 2. Reference numerals 1 to 3 describe the multilayer laminate as shown in FIG. This multilayer laminate is placed on the preferably heated thermoform 4 and pressed after heating with compressed air (5) in the recesses of the thermoform.

Finally, the invention also relates to the use of multilayer laminates, as described in the context of this document, for the production of membranes for electroacoustic transducers.

The following example is intended to explain the invention without wishing to limit it. Example 1 The amorphous PEEK film Aptiv 2000-006GS from Victrex, thickness 6 μm, is coated with an acrylate adhesive in a layer thickness of 20 μm and then dried at 120 ° C. for 5 minutes. Then, the partially crystalline PEEK film Aptiv 1000- 008GS, thickness 8 μηη, applied to the adhesive layer and laminated by pressing with a roller bubble-free. From this multi-layer laminate, an approximately 10 cm by 10 cm large area is cut out and placed on the thermoforming that the amorphous PEEK film lies on the heated embossing mold and the semi-crystalline film facing upward. Subsequently, the laminate is heated in the thermoforming and pressed by applying pressure in the form of the finished membrane. In contrast to multilayer laminates of two 6 to 9 μηη thick amorphous PEEK films with adhesive layer therebetween, the problem of wrinkling in the upwardly facing and the compressed air facing PEEK film does not occur.

Claims

claims

Multilayer laminate for the production of membranes for electroacoustic transducers, comprising

a first layer ("first cover layer") of a polyether ether ketone film ("PEEK film") having a heat of crystallization of at least 15 J / g, determined in the first heating curve of the differential scanning calorimetry measurement,

- A second layer ("second cover layer") of a thermoplastic film having a heat of crystallization of at most 5 J / g, determined in the first Aufheizkurve the differential scanning calorimetry measurement, and

- An arranged between the first and second cover layer adhesive layer.

a first layer ("first cover layer") which has a shrinkage greater than 10% after 15 minutes at 200 ° C. in at least one direction,

- A second layer ("second cover layer"), which after 15 minutes at 200 ° C in the longitudinal and transverse directions each have a shrinkage of less than 10%, preferably less 5%, and

- An arranged between the first and second cover layer adhesive layer.

Multilayer laminate according to one of the preceding claims, characterized in that

the second cover layer consists of an at least partially crystalline PEEK film.

Multilayer laminate according to claim 1 or 2, characterized in that the second cover layer consists of a plastic whose main component is selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyetherimide, polyimide, polyarylate, polyphenylene sulfide, polyphenylsulfone, polysulfone, polyethersulfone. Multilayer laminate according to one of the preceding claims, characterized in that

the layer thicknesses of the two outer layers in each case 1 μηη to 50 μηη, preferably 2 μηη to 40 μηι, more preferably 5 μηη to 15 μηη amount.

the layer thickness of the adhesive layer 2 μηη to 100 μηη, preferably 5 μηη to 50 μηη, more preferably 10 μηη to 30 μηη.

A process for producing membranes for electroacoustic transducers from a multilayer laminate according to any one of claims 1 to 6 by means of multicavity thermoforming.

Use of multilayer laminates according to one of claims 1 to 6 for the production of membranes for electroacoustic transducers.